Psychology's long and distinguished history on measurement of human behavior laid the foundation for counseling psychology's emphasis on person-environment interaction. Without measurement there can be no science. Equally important to the development of this emphasis was the much slower recognition and subsequent measurement of the effects of environment on human behavior. Within the various disciplines of psychology, too often those assessing personality have ignored the work of those studying environmental influences, and vice versa. Psychologists in applied practice have gradually realized, perhaps sooner than basic researchers, that behavior is not only a function of individual differences and environment but that the two have a reciprocal relationship. Persons affect environments just as environments affect persons. Only now are research and intervention strategies being developed that truly incorporate this interactive thinking.